Real-Time Chemical Sensing for Advanced Process Control in ALD Gary W. Rubloff 1, Laurent Henn-Lecordier 2, and Wei Lei 3 University of Maryland 1 Director, Maryland Center for Integrated Nano Science and Engineering, and Minta Martin Professor of Engineering, Department of Materials Science & Engineering, Institute for Systems Research, and Institute for Research in Electronics and Applied Physics, www.isr.umd.edu/gwrubloff, rubloff@umd.edu 2 Department of Materials Science & Engineering and Institute for Systems Research 3 Department of Materials Science & Engineering and Institute for Systems Research. Current address: Novellus Systems
Delivering Value from ALD Research Real-Time Chemical Sensing ALD Process Dynamics ALD Metrology Advanced Process Control Development Manufacturing 2
Atomic Layer Deposition a simple picture an ideal process Initial surface Metal precursor exposure Purge BUT Nucleation & surface condition dependence OH OH OH SUBSTRATE L L L M L L L M L L L L M L OH OH O LH L L L L M L L M L L M L O O O Temperature-dependent growth Dose dependencies Monolayer growth OH M OH OH O M O M O O O Purge H 2 O LH H 2 O H 2 O OH OH L OH M O M L L M L O O O Reactant B exposure Incomplete layer adsorption & reaction Multilayer adsorption & reaction 3
Moving ALD to Manufacturing Nucleation & surface condition dependence Temperature-dependent growth Dose dependencies Incomplete layer adsorption & reaction Multilayer adsorption & reaction Advanced process control (APC) required for manufacturability Course correction Fault management Sensors needed for APC Process chemistry Wafer state Sensors needed for process learning Chemical complexity Process metrology 4
Real-Time Chemical Sensing Real-time mass spectrometry (MS) for wafer-scale ALD process Direct observation of process dynamics Integrated MS signals cycleby-cycle Integrated MS signals through entire run Comparison with ex-situ film characterization Process recipe optimization Nucleation & growth kinetics Thickness metrology & control Process-film properties correlation & prediction 5
Embedded ALD Mini-Reactor Z-axis pneumatic actuator UHV chamber 10-5 torr Moveable cap 5 torr 100 mm wafer Substrate heater Differentially pumped MS 35 µm orifice Gas Outlet Gas Inlet ALD mini- reactor 6
ALD System and Process Sensing 300 amu CIS mass-spec 100 mm wafer, substrate-heated UHV ALD reactor 35 µm orifice 5 Torr Load-lock UHV-ALD 1.2x10-10 1.0x10-10 Differential pumping Gas Outlet Gas Inlet Intensity (A) 8.0x10-11 6.0x10-11 4.0x10-11 MS in-situ sensing (10 ALD cycles) Precursors: WF 6, SiH 4 SiH 4 exposure H 2 product WF 6 exposure SiF 4 product MS response time: < 1 sec 2.0x10-11 13:59:56 14:01:22 14:02:48 14:04:14 14:05:40 14:07:06 14:08:32 Time 7
ALD Process Dynamics 1.2x10-10 1.0x10-10 10 CYCLES - 325 8.0x10-11 Intensity (A) 6.0x10-11 4.0x10-11 2.0x10-11 13:59:56 14:01:22 14:02:48 14:04:14 14:05:40 14:07:06 14:08:32 Time 6.0x10-11 5.0x10-11 SiH 4 exposure H 2 1 CYCLE - 325 Purge WF 6 exposure Purge Precursors: WF 6, SiH 4 SiH 4 exposure H 2 product WF 6 exposure SiF 4 product MS response time: < 1 sec Intensity (A) 4.0x10-11 3.0x10-11 2.0x10-11 1.0x10-11 SiF 4 SiH 4 SiF 4 0 10 20 30 40 50 60 70 Time (Sec) 8
Optimizing ALD Process Recipe Intensity (A) Intensity (A) 7.0x10-11 6.0x10-11 5.0x10-11 4.0x10-11 3.0x10-11 2.0x10-11 1.0x10-11 6.0x10-11 5.0x10-11 4.0x10-11 3.0x10-11 2.0x10-11 SiH 4 exposure SiH 4 0 10 20 30 40 50 60 70 H 2 SiH 4 Purge Time (Sec) WF 6 exposure SiF 4 Purge Reference 60 C Process 325 C Surface reaction time Intensity (A) Reactants 6.0x10-11 4.0x10-11 2.0x10-11 H 2 H 2 SiH 4 SiF 4 WF 6 By-products Process recipe optimization SiH 4 Purge WF 6 SiF 4 Purge 1.0x10-11 0 10 20 30 40 50 60 70 Time (Sec) 0 10 20 30 40 50 Time (s) 9
Validation by Ex-Situ, Post-Process Process Characterization 2.0 Gas flow direction Exposure (s) SiH 4 / WF 6 Gas Inlet Gas Outlet Film thickness (μm) 1.5 1.0 0.5 Precursor depletion 15 / 20 s 10 / 8 s * 8 / 6 s 5 / 4 s Ex-situ 4 point probe measurements 0 20 40 60 80 100 Position Across the Wafer (mm) 10
ALD Metrology Real-time metrology: integrate product signals over each pulse 1.2x10-10 Identify pulse-to-pulse trends nucleation kinetics 1.0x10-10 Intensity (A) 8.0x10-11 6.0x10-11 4.0x10-11 Integrate signal over all pulses total deposition thickness 2.0x10-11 13:59:56 14:01:22 14:02:48 14:04:14 14:05:40 14:07:06 14:08:32 Time 10 CYCLES - 325 11
Real-Time Growth Kinetics 4.0x10-10 Nucleation regime Linear growth regime 1.2x10-9 Nucleation regime Linear growth regime Integrated SiF 4 Signal Per Cycle 3.5x10-10 3.0x10-10 2.5x10-10 2.0x10-10 1.5x10-10 1.0x10-10 5.0x10-11 SiF 4 by-product Integrated H 2 MS Signal Per Cycle 1.0x10-9 8.0x10-10 6.0x10-10 4.0x10-10 2.0x10-10 H 2 by-product 0 10 20 30 40 50 60 70 80 Cycle Number 0 10 20 30 40 50 60 70 80 Cycle Number Precursors: WF 6, SiH 4 SiH 4 exposure H 2 product WF 6 exposure SiF 4 product MS response time: < 1 sec 12
Validation by Ex-Situ, Post-Process Process Characterization Integrated H 2 QMS Signal Per Cycle (A*Sec) Integrated MS signals over 1 ALD run 1.2x10-9 1.0x10-9 8.0x10-10 6.0x10-10 4.0x10-10 2.0x10-10 4-pt probe thicknesses over 6 ALD runs 0 0 10 20 30 40 50 60 70 80 90 ALD cycle number 100 80 60 40 20 Film Thickness (nm) 13
Initial Surface Condition Nucleation region for HF-last treated surface Nucleation region for H 2 O-last treated surface Integrated SiF 4 MS Signal Per Cycle 6.4x10-10 5.6x10-10 4.8x10-10 4.0x10-10 3.2x10-10 2.4x10-10 1.6x10-10 8.0x10-11 HF Treated Surface H 2 O Treated Surface 0 10 20 30 40 50 60 70 80 Cycle Number 14
Temperature Dependence Nucleation and growth both increase with temperature Integrated H 2 Mass Spec Signal Per Cycle 2.5x10-9 2.0x10-9 1.5x10-9 1.0x10-9 5.0x10-10 325 C 250 C 175 C H 2 during SiH 4 half cycle 0 10 20 30 40 50 Cycle Number 15
Temperature Dependence Ex-situ SIMS results Intensity (A) 4.0x10-10 3.2x10-10 2.4x10-10 1.6x10-10 8.0x10-11 SiH 4 Exposure H 2 signal 175 Purge 225 275 325 0 20 40 60 80 100 120 Scan Number WF 6 Exposure SiF 4 signal Purge CsW Counts Integrated SiF 4 Signal Per Cycle 4x10 4 3x10 4 2x10 4 1x10 4 3*10-10 2*10-10 10-10 0 0 20 40 60 80 100 MS Depth (nm) 1.6 1.8 2.0 2.2 1000/T (K -1 ) SIMS 175 225 275 325 10 Growth Rate (A/Cycle) 1 16
Real-time Wafer State Metrology W Film Thickness (nm) 35 30 25 20 15 10 5 5 consecutive wafers (225 C) 1st wfr (175 C) (175 C) (325 C) (275 C) 8.0x10-9 1.6x10-8 2.4x10-8 3.2x10-8 4.0x10-8 Sum of Integrated SiF 4 Signal W Film Thickness (nm) 100 80 60 (275 C) 40 20 1st wfr (275 C) 0 2.0x10-8 4.0x10-8 6.0x10-8 Sum of Integrated SiF 4 Signal (325 C) Without pre-process chamber treatment With pre-process chamber treatment 1 st wafer effect associated with surrounding walls of mini-reactor 17
Origin of 1 st Wafer Effect 1.2x10-9 2 nd wafer Gas Inlet Gas Outlet QMS sampling Integrated H 2 Signal Per Cycle 9.0x10-10 6.0x10-10 3.0x10-10 1 st wafer H 2 during SiH 4 half-cycle 0 10 20 30 40 50 60 70 80 Cycle Number Product signals for 1 st wafer include nucleation on wafer and surrounding environment Product signals for subsequent wafers correspond to nucleation only on wafer 18
Precursor Dose Interactions 2.0x10-10 SiH 4 Exposure H 2 signal Purge WF 6 Exposure SiF 4 signal Purge WF 6 : 5 sccm H 2 signal 1.5x10-10 SiF 4 signal Intensity (A) 1.0x10-10 Increase WF 6 concentration WF 6 : 1 sccm H 2 signal SiF 4 signal 5.0x10-11 Increase WF 6 concentration 0 20 40 60 80 100 Scan Number WF 6 exposure influences SiH 4 exposure Precursor exposure interactions are important in ALD (imperfect self-limiting behavior) Higher concentration higher reaction rate shorter reaction time 19
Combinatorial CVD Spatially programmable showerhead gas delivery enables combinatorial chemical vapor deposition 20
Combinatorial ALD Numerous process recipe permutations in real-world ALD Precursor dose interactions Ternary (& higher) materials systems Sr precursor Ti precursor H 2 O oxidant 21
Conclusions Challenges for ALD manufacturing: Deviations from perfect layer-by-layer growth Dependence on reactant dose, temperature, surface condition Diversity and complexity of materials systems and applications Real-time chemical sensing provides direct insight into ALD process mechanisms and dynamics. Sensors can be employed for process optimization, process and wafer state metrology, and advanced process control for manufacturing. Real-time sensors and combinatorial strategies may be essential in managing the complex subtleties of atomic layer deposition 22
Acknowledgements Support Students Wei Lei, Laurent Henn-Lecordier Erin Robertson, Rama Sreenivasan Faculty Ray Adomaitis 23
Real-Time Chemical Sensing for Advanced Process Control in ALD Self-limiting surface chemistry endows atomic layer deposition (ALD) with exceptional benefits, from atomic-level control to unprecedented conformality and uniformity in chemically deposited thin films. However, the transition into mainstream manufacturing imposes new demands for advanced process control, and in turn integrated sensors to achieve that control. We have explored these questions using several sensor techniques, particularly downstream quadrupole mass spectrometry (QMS), QCM, and FTIR within the context of a wafer-scale reactor serving as a manufacturing prototype. Realtime signals reveal the dynamical phenomena during ALD half-cycles and surface chemistry on the wafer, including dose interactions indicating imperfect self-limiting reaction, temperature dependence, and depletion. Metrology derived from dynamic sensor signatures provides rapid observation of nucleation kinetics. Dynamic chemical sensing is thus poised to enable ALD manufacturability and process control. To facilitate ALD process development for complex materials (ternaries, etc.), we are also pursuing combinatorial methods for ALD as an extension of our combinatorial CVD research. 24